1. Field of the Invention
The present invention relates to a laminated multi-layer circuit board that is formed into a single body under heat and pressure.
2. Description of Related Art
A method of forming a laminated multi-layer circuit board has been known hitherto. One exemplary method is disclosed in JP-A-2006-49502. In the known method, insulating layers made of thermoplastic resin and conductor layers each having a circuit pattern are alternately laminated to form a laminated body. Then, the laminated body is pressed under heat to form an integral body of the laminated multi-layer circuit board. In the pressing process, a buffer member is interposed between the laminated body and a hot press plate to apply a pressure uniformly to the laminated body. The layers are electrically connected by an inter-layer connector formed in a via-hole formed between neighboring conductor layers.
In the process forming the integral body of the multi-layer circuit board by applying pressure and heat to the laminated body, applied pressure is not uniform on the entire surface of the laminated body. This is because a larger number of circuit patters are formed at a certain place compared with other places, and the inter-layer connecting portions are not uniformly formed. By placing the buffer member between the laminated body and the hot press plate, a pressure is adjusted to be applied uniformly to the laminated body to a certain degree. However, there remains a considerably high imbalance of pressure applied to the laminated body. There is a possibility that the thermoplastic resin to which too high heat and pressure are applied flows to other places where less pressure and heat are applied. This deforms the circuit patterns, making the circuit board less reliable.